The invention relates to a pulse code modulation (PCM) regenerator that is more particularly described as a regenerator having automatic gain control (AGC) referenced to a data-pattern-dependent pulse stream.
It is well known that a PCM system reconstructs a transmitted pulse train after it has traveled through a dispersive, noisy medium. This process is referred to as pulse regeneration and includes retiming of the pulses and regeneration of their amplitudes. The process includes deciding whether the signal amplitude is above or below some threshold at the sampling time. Linear amplifiers are used for equalizing and noise band limiting the transmitted pulse stream.
Because deviations of amplifier gain from nominal gain can cause degradation, automatic gain control (AGC) is needed in regenerator circuits. Although it is desirable to use a steady reference tone from received signals for developing an AGC signal, there is no naturally occurring steady tone in the pulse stream of any practical PCM system. Instead the spectral content of the pulse stream is dependent upon the pattern of the pulse stream being transmitted. An examination of known pulse stream patterns shows that the shapes of their power spectra are quite different from one another. Since any one of several known pulse patterns can be transmitted on a PCM line at any time and for any deviation, no amount of statistical or time averaging can reduce the range of spectral amplitudes.
Various methods for stabilizing a regenerator have been described in the literature. One such method is described in U.S. Pat. No. 3,404,232, issued Oct. 1, 1968 in the name of T. M. Burford. Such patent discloses the use of amplitude correcting signals generated by plural secondary amplitude sensing circuits to adjust the gain of a signal amplifier.
The plural secondary amplitude sensing circuits produce discrete steps of amplitude units whenever correction of an input signal is indicated regardless of the actual magnitude of the deviation of the input signal. Finer control can be achieved with the prior art arrangement by adding to the complexity and the cost thereof. It is, however, more desirable to achieve finer control with an arrangement that is simple and inexpensive.
It is an object to develop a PCM regenerator using an automatic gain control signal that is derived from the data-pattern-dependent pulse stream.
It is another object to develop a simple and economical automatic gain control arrangement which achieves fine control.